A seat belt system is typically anchored to a vehicle at three different locations around a vehicle passenger. Two anchors support the lap belt portion of a seat belt while a third anchor, a loop or D-ring, located at the approximate height of the shoulder of the passenger provides support for the shoulder belt portion of the seat belt. Due to varying sizes of passengers, manufacturers use assemblies known as adjustable turning loops, which allow the shoulder loop to be adjusted up or down to accommodate these differing heights. Existing adjustable turning loops typically comprise a slide that mounts the D-ring to a rail, which is attached to the B pillar of the vehicle. The slide may be adjusted up or down by lifting or pressing an actuator, which releases a lock that holds the slide in place. The locking mechanism is frequently very complex and expensive to manufacturer and assemble. A need therefore exists for a simplified locking mechanism for an adjustable turning loop.